There are a handful of surface signs that something is going wrong with your body; if your hair starts falling out, your skin gets red and flaky, or your eyes become discolored, you know you should see your doctor right away. Yet, there is one other home-grown tool to help you determine whether your health is out of whack: your nails.

In many ways, your fingernails are excellent diagnostic instruments. Because they grow so quickly, they can tell you (and your doctor) almost exactly what is going on inside you, and you can receive the treatment you need to feel better faster. Here are a handful of nail-related signs and symptoms that could mean something is seriously wrong with your health.

Brittle Nails

Like your hair and skin, your nails can lose their strength and become dry and brittle. Not only do dry, brittle nails look unappealing, but they are also at a higher risk for cracking, which is extremely painful and can take some time to heal.

Sometimes brittle nails are the result of vitamin deficiency ― particularly vitamins A, C, or biotin ― but more commonly, your nails are peeling and cracking thanks to your lifestyle. If you spend much of your time with your hands in water, using harsh chemicals (including nail polish remover), or dwelling in regions with high humidity, you could develop brittle nails. At the very worst, your brittle nails are symptoms of a serious thyroid disease, and you should visit the doctor immediately.

Clubbed Nails

Clubbing is a condition that pertains to fingers and toes, but most people first notice clubbing by changes to their nails. If you are experiencing clubbing, the tips of your digits might start to enlarge and turn red and warm, which will cause your nail to curve downward and your cuticles to stick out at an odd angle.

Clubbing is always evidence of low oxygen in your blood, which is incredibly dangerous. Usually, when a doctor sees clubbing, he or she diagnoses serious heart or lung diseases, which require substantial lifestyle changes to overcome.

Curved Nails

Also called “spoon nails,” nails the curve upward at the edges are inconvenient as well as unattractive. When your nails are snagging at fabric, scratching wood and paint, and even wounding yourself, you need a fix fast.

Fortunately, curved nails are most often associated with anemia, which is a simple iron deficiency. Consuming more iron, either in your diet or through supplements, should resolve your problem. However, if the curving persists, you should see your doctor about potential heart or thyroid issues.

Spotted Nails

White spots anywhere else on your body might be a cause of concern, but when you see white spots on your nails, you don’t need to worry at all. The spots are called “leukonychia,” and despite popular believe that they signal a calcium deficiency, they actually are the result of some long-past minor trauma to your nail bed. As your nail grows out, the spots should disappear on their own.

Ridged Nails

Nail ridges form according to a person’s DNA, which means for the most part, your ridges are a natural and unique part of you. Vertical ridges in particular are a common development of aging and pose absolutely no cause for concern.

However, white horizontal ridges, known as Mees’ Lines, have several acute and chronic causes which you might want checked by a doctor. Most often, horizontal ridges are due to the same type of trauma that causes harmless white spots, but illnesses that cause high fever, like pneumonia or scarlet fever, can also bring about ridges in the nails. However, Mees’ Lines are also caused by long-term arsenic poisoning, carbon monoxide poisoning, and other potentially unknown health problems that require immediate medical attention.

Conversely, your horizontal ridges might take the form of Beau’s Lines, which look more like deep grooves in the nail. In this case, you could be suffering from an underlying, untreated disease, like diabetes, psoriasis, or a circulation problem that requires medicine to remedy.

Yellow Nails

Usually, nails turn yellow thanks to stains in your environment. If you constantly paint your nails or use acrylics, your nails will eventually turn yellow. Alternatively, smoking is a common cause of yellow nails because the tar in tobacco and smoke adheres to the fingers holding the cigarettes. In both cases, taking a break from the activity will give your nails a chance to clean up. If smoking is your vice, you can make a switch to smokeless e-cigarettes while your nails regrow. In addition, taking B12 supplements helps to hasten nail growth so your stains don’t last long.

White Nails

It’s natural that your nails have a strip of white at the ends, but when your entire nails turn white with a strip of pink at the top, you must see your doctor immediately. Called Terry’s Nails, this inversion of healthy nail color is a sign of your organs shutting down. In particular, white nails signal heart, liver, kidney, and pancreas failure, and you need all of those to survive.